JPS60138401A - System and device for measuring absolute length of transmission line - Google Patents

Abstract

PURPOSE:To obtain an exact measured value of an absolute length by deciding the polarity of an instruction of a phase measuring system for sweeping successively and displaying a modulation section which has set the upper limit and the lower limit, counting the number of times which has exceeded 2pi, and deriving an absolute phase quantity. CONSTITUTION:A modulating part A fetches a reference signal and a signal for passing through a transmission line to be measured, from a front light and a back light of a semiconductor laser. Subsequently, in a demodulating part B, a signal which has passed through an optical fiber 3 is converted to an electric signal by an optical-electric transducer 4, and thereafter, mixed with an output frequency of the second wave oscillator 10, a hybrid 11 of 3dB branch, and a directional coupler 12 by a frequency mixer 13. This intermediate frequency fIF passes through BPF5 and becomes a signal to be measured VS. Also, the reference signal is dropped as well to the intermediate frequency fIF by an optical-electric transducer 4' and a frequency mixer 13', and becomes a reference signal VR through a BPF5'. A measuring part C is constituted of a phase measuring instrument 7, and displays a phase quantity not exceeding 2pi. Also, a display of the phase measuring instrument 7 of every sweep frequency is read to a control part D.

Description

Detailed Description of the Invention (Field of Application) The present invention relates to a method for measuring the absolute length of a transmission line and a device used for the measurement, and in particular, the present invention relates to a method for measuring the absolute length of a transmission line and a device used for the measurement. It concerns a method and device for measuring length.

(Prior Art) Knowing the transmission characteristics of a long-distance transmission system is important for effective line use and is an extremely important problem in constructing a long-distance transmission system.

By the way, in the past, the approximate absolute length of the transmission line was calculated based on the route of the transmission line. The absolute length was measured by calculating the phase difference and converting it.

However, the absolute length value obtained from the former measurement method had a large error, and it was not possible to obtain an accurate value. On the other hand, in the latter measurement method of measuring and converting the phase amount to calculate the absolute length, it is difficult to easily measure the phase amount of 2π or more, so it is difficult to calculate the accurate value. Ta.

In other words, if the absolute phase 1t (2π x integer multiple + θ) is calculated, the absolute length can be calculated by dividing it by the radio wave propagation speed (3X 10' rnS). (2) It was difficult to determine the exact absolute length because it included the phase difference (constant value) that occurred inside the measuring instrument system.

As is clear from the above explanation, it is nearly impossible to determine the exact absolute length using conventional measurement methods.

(Purpose) The purpose of the present invention was made in view of the drawbacks of the prior art described above. The purpose is to provide a method and device for doing so.

(Generally, the feature of the present invention is that the upper and lower limits of the modulation frequency are set, and the polarity of the indication of the phase measurement system displayed by sequentially sweeping the modulation section is determined, and the number of times the frequency exceeds 2π is calculated. The point is that the absolute phase member is determined by counting and the absolute length is measured.

Another feature of the present invention is that, as shown in FIG.
a demodulating section B for converting the signal into a signal; a measuring section C for measuring the phase difference between the two signals; a means for controlling the frequencies of the modulating section A and the demodulating section B; The present invention is characterized in that it is equipped with a control section consisting of means D2 for determining, means for calculating an absolute phase amount, and means D4 for calculating an absolute length from the absolute phase amount.

(Example) Here, in the method of measuring the absolute length of an optical fiber, the modulation frequency is particularly high and the absolute phase amount (2πX integer times 10) (
However, θ is the remainder when the amount of phase change is divided by an integer multiple of 2πX)
For example, when v becomes large and difficult to measure, v,'
The present invention will be explained in detail using the drawings below.

FIG. 2 is a block diagram for explaining the basic principle of the present invention. In the figure, l is a first sine wave oscillator for oscillating modulation frequency f, 2 is a semiconductor laser, 3 is an optical fiber of the transmission line to be measured, 4 is a photoelectric converter, and 5 is a bandpass filter (hereinafter referred to as (Abbreviated as B, P, F) v, C Measured A No. 6 and 7 are phase measuring devices, and vR is a reference signal.

In the figure, Δθ is the reference signal ■8 and the sine wave oscillator 1→
Semiconductor laser 2 → optical fiber 3 → photoelectric converter 4 → B,
This means the phase difference (absolute phase Il) with the signal under test v8 that has passed through P and F5, and is expressed as equation (1).

In equation (1), the first term (Δθ.) conet is an error within the measuring instrument system that occurs even when there is no optical fiber 3 in the transmission line to be measured. C is the speed of light in vacuum, and f is the modulation The frequency, N, is a constant determined by the state of stress (mainly tension) applied to the fiber under test (N => 1.46 to 1.47
), L is the optical fiber length of the optical fiber 3.

Next, when the modulation frequency f is changed to f', the phase difference Δθ' is expressed by equation (2).

Therefore, the difference δθ between Δθ and Δθ' is given by equation (3).

As is clear from equation (3), the absolute length of an optical fiber can be measured by calculating the phase difference between two different frequencies. The measurement resolution for length can also be set arbitrarily with a difference of 1-1'.

Based on the above basic principle, it is possible to measure the absolute length by measuring the absolute phase difference between two different frequencies, but with a normal phase measuring device 7, the phase difference of (2π × integer multiplier + θ) is calculated from θ. only is displayed and the absolute phase difference cannot be measured. therefore
If the frequency difference f - f' is made very small, the phase difference δθ
Although L can be kept within 2π, the measurement resolution deteriorates, making it impossible to accurately measure the absolute length.

Therefore, in order to measure the absolute length with high precision, it is necessary to have good measurement resolution and to include the absolute phase difference (2π × n + θ) (where n is an integer). This will be explained using figures.

In FIG. 3, the horizontal axis represents the modulation frequency f, and the vertical axis represents the indication δθ' of the phase measuring instrument when the phase difference displacement δθ1 at the modulation frequency f is based on the phase difference Δθ at the modulation frequency fmin. . However, as mentioned above, the indication δr of the phase measuring instrument is a value within ±π, and δθ′ is δ
It is the value of the remainder when θ is divided by 2π.

Therefore, the frequency Δf=fmax −f that satisfies the desired measurement resolution in measuring the absolute length of the optical fiber is
When min is selected, as shown in the figure, fmin and '
m modulation frequencies fk (k=1.2...
........., m), and δθk (k=
1.2. .

′, that is, δθ1=2π” max 'min)
NL/C=2π(f, -fm,,) NL/C+
2π(f2- f,)NL/C+ ・・・・・・・・・
+ 2 π (fk-f, 1) NL/C 10...song -
...+2゛π(frrlax-fm)NL/c=
δθ1+δθ2+ ・−、、、、、＋＋δθ＋・・・
・・・・・・+60m+1, 2 frequencies fmlL
If you sweep the frequency f between X and fmin, the absolute phase difference δ9 will be 1! It can be placed on one's back, and by converting δθ, the absolute length of the optical fiber can be measured.

However, if the absolute phase difference δθ is determined by adding up the individual phase difference displacements δθ□ using the method described above, measurement errors of each measurement value will be accumulated and the accurate absolute phase difference δθ will be calculated.

may not be measurable. Therefore, the modulation frequency fk (k=1, 2, . . . r m )
is used to determine the polarity (positive or negative) of the indication δd of the phase measurement system, and the number n of 2π is calculated from the number of polarity changes.
used to determine.

For example, as shown in Fig. 3, K within a change of π, for example, three frequencies are set, and when the sign of the phase measurement system indication δθ' changes from + to -, 2π is exceeded once. Then, the number of times n of 2π at the modulation frequency fmax is measured.

Also, the number n of 2π may be determined as follows, that is, by setting three frequencies within the change of π, r-, +
, −, shi, shi, shi, when the sign of J comes, the phase difference displacement is 2π
2π up to the modulation frequency fmax.
Measure the number of times n.

Therefore, the absolute phase difference δθ1 is expressed by the following equation (4).

δθ, −(2π×n+θ) ・・・・・・・・・・・・
......+41 (where θ is the 7it final indication value of the phase measuring device) Also, the absolute length of the transmission path can be accurately determined from the following equation.

L=δθ, X C/2πXN×(frllaX−fm
in) Curved surface (5) In this way, in the present invention, by setting the modulation frequency width Δf='max-fmin and sweeping the range with the modulation frequency fk, the absolute value of the optical fiber can be determined with high resolution. Can measure length.

Next, an absolute length measuring device #t using the principle of the absolute length measuring method according to the present invention will be explained.

FIG. 4 shows an embodiment of an optical fiber absolute length measuring device according to the present invention.

In the figure, A is a modulation section, B is a demodulation section, C is a measurement section,
D is a control section, E is an optical fiber 3 as a transmission medium to be measured, and the apparatus of this embodiment is composed of four sections A to D. Note that 15 is an output terminal device (for example, a digital printer or display) iHll.

A's strange! Part 11 is composed of a first sine wave oscillator 1 whose frequency can be varied from 'min' to 'max, and a semiconductor laser 2 whose output light is modulated by the oscillator 1. In order to eliminate measurement errors due to the temperature characteristics of the semiconductor laser, the modulation section A extracts the reference signal and the signal passing through the transmission line to be measured from the front light and rear light of one semiconductor laser, and eliminates the influence of temperature changes on the semiconductor laser. are offsetting.

Note that a beam splitter may be used as a method of extracting two output lights from one semiconductor laser.

Next, the demodulation section B can be roughly divided into a demodulation section for the reference signal and a demodulation section for the signal that has passed through the transmission line under test, but since the configuration of the apparatus is the same, the demodulation section on the transmission line under test side will be explained.

First, a signal that has passed through the optical fiber 3, which is the transmission line to be measured, is converted into an electrical signal by the opto-electrical converter 4. Thereafter, the electrical signal (frequency f, ) is converted into an RF flaw signal IF (
The output frequency f of the 10.3 dB branched hybrid 11 and the directional coupler 12 is mixed by the frequency mixer 13 to produce an intermediate frequency 'IF''. "l'! is converted to This intermediate frequency 'IF passes through B, P, F, and 5 to become the signal under test V. Although the frequency of the signal to be measured V is fIF, it goes without saying that the phase shift 2πf, NL/C that occurs when propagating through the optical fiber does not change.

Similarly, the reference signal is converted into an electrical signal by the opto-electrical converter 4', and then converted to an intermediate frequency 1 by the frequency mixer 13'.
You will be taken down to the 1st floor. Then B, P, F.

5' and becomes the reference signal vR.

Here, the reason for measuring after lowering the frequency to the intermediate frequency fIF will be explained.

Usually, the phase measuring device 7 has a fixed band for the received signal.
With only one tuning band, it is not possible to cover the entire sweep frequency width when sweeping from fmin to fm&min as in the present invention. Another reason is that it is better to pass the IF multiplied signal through the narrow band B, I), F, 5°5' to remove band noise, rather than passing the RF flawed signal as it is through B, P, F, 5.5'. It is possible to obtain a large S/N ratio.

Therefore, if the frequency is converted and then input to the phase measuring device 7 as in this embodiment, even if the modulation frequency of the signal is varied from several MHz to several hundred M
Automatic measurement becomes possible without the need to change the tuning band each time. Furthermore, there is an advantage that the S/N ratio can be improved even if the reception level of one word is low.

The measurement part of C is made up of (1q) with phase 61 and foot temperature 7,
It displays the phase amount within 2π. As mentioned above, the relationship between modulation frequency f and Ic < constant intermediate frequency 1
Since the signals V, , and VR converted into are the input F signals, all can be measured in one P1 band. Further, the display of the phase measuring device 7 for each sweep frequency is read into the control section described below.

Finally, the control section of D is a control circuit 14 using a microcomputer or the like.
It is.

The function of this control circuit 140 will be explained with reference to the flowchart shown in FIG.

Step S1: Data on the liver oil refraction index M of the optical fiber and the approximate length of the fiber are input to the control circuit 14.

Step S2... Set the phase measuring device 7 remotely,
The manual operation of the measuring instrument 7 is canceled. Then, the measuring device 7 is connected to the control circuit 14.

Step S3...The maximum modulation frequency aFm is determined by dividing the maximum frequency F8 of the sine wave oscillator l by the approximate length of the fiber. In addition, by dividing a constant A determined from n degrees of measurement by the product of the approximate length of the fiber and the maximum number of sweeps N, the maximum frequency Fm and the required sweep interval ΔF can be controlled to calculate the sweep interval ΔF. It is set in the circuit 14.

Step S4...The number n of 2π is reset to O.

Step S5...The current number of sweeps 1 is the maximum number of sweeps N
Make a judgment as to whether it is equal to or not. If no, proceed to step S6; if yes, proceed to step S815.

Step S6... variable second sine wave oscillator 10
0 frequency (local oscillation local wave number) f2 and the oscillation frequency f1 of the first sine wave oscillator 1 are set. The oscillation station wave number and fl are determined by the following equation.

f,=F,-(N-I)ΔF fI=’! +’IF However, fIF does not include intermediate frequency a.

Step S7: Read the current phase difference S1 measured by the phase measuring device 7.

Step 8B: An angle θ at which the absolute value of the difference between the previously measured phase difference S2 and the current phase difference S1 is determined in advance. A determination is made as to whether the value is greater than or not. If no, proceed to step S9; if yes, proceed to step S11. Note that the angle θ. The final cost is 600. Zoo.

etc. are suitable.

Step S9: The 111th phase difference s2 is updated to the current phase difference S1.

Step 810: Add 1 to the number of sweeps.

Steps 811, 812...A determination is made as to whether the sign of the phase difference 81 has changed from positive to negative, continuously changed from negative to positive, or whether these two changes have not occurred.

When the sign of the phase difference S1 changes from positive to negative, the process proceeds to step S13; when the sign changes from negative to positive, the process proceeds to step S14.

Moreover, when it is neither of these, it progresses to step S9.

Step S13: Add 1 to the number n of 2π.

Step 814: Subtract 1 from the number n of 2π.

The processes of steps 85 to 814 are performed until the answer is YES in step S5. As a result, the oscillation frequency 11 of the first sine wave oscillator 1 is changed to Fm-(N-1)ΔF+f1
F(=frnln) to Fm-ΔF” 'IF (=i
m! The number of times n of 2π when changing up to LX ) is rounded.

Step S15... Determine the absolute phase difference δθ from the number n of 2π and the measured value θ of the phase measuring device 7, and calculate the optical fiber length L (1) j from the above equation (5).

Note that at this time, δθL=2πntoθ.

Step 816...The output terminal device 15 is made to output the result determined in step S15.

Step 817: The phase measuring device 7 is set locally, and the tk phase measuring device 7 is restored so that the phase difference can be measured manually.

(Effect) As described above, according to the method of the present invention, the absolute phase amount δ
Since it is possible to accurately calculate the absolute length of the wired transmission line.

The apparatus of the present invention also includes a means for selecting a modulation frequency width Δf (-f −f・ ) that satisfies a desired measurement resolution, and a means for converting the frequency of the reference signal and the signal under test for use in a phase measuring instrument. Since it has means for adjusting to the tuning band, it is possible to automatically measure the absolute phase amount of 2π or more with high resolution and precision without changing the tuning band of the phase measuring device each time.

Although the explanation here uses an example of an optical fiber measurement device with a high modulation frequency and an absolute phase amount of 2π or more, it can also be applied to ground transmission media such as coaxial cables.
Moreover, it can be applied to a device that not only measures the absolute length from the absolute phase amount but also measures delay characteristics.

As described above, in the present invention, the absolute phase amount can be measured accurately and easily, which is extremely important for understanding transmission path characteristics. Moreover, as a result, maintenance and cleaning of the wired transmission line becomes easier, which has a great effect.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram of the present invention, FIG. 2 is a principle diagram of the present invention, FIG. 3 is a diagram for explaining the present invention in detail, and FIG. 4 is a block diagram of an embodiment of the present invention. FIG. 5 shows a flowchart for explaining the functions of the control section in FIG. 4. 1... First sine wave oscillator, 2... Semiconductor laser, 3
・Optical fiber to be measured, 4,4'・Optoelectric converter, 5.5
'... Bandpass filter, 7... Phase measuring device, 9
...Second sine wave oscillation: 11.Hybrid, 12.Directional coupler, 13.Frequency mixer,
14...control device, A...modulation section, B...abdominal tone section, C...measuring section, D...patent attorney representing Abe Michi Hiraki 1 non-human talent 1 [Ne1 Fang 2 (! 1 1/3 Figures 4 Figures

Claims (2)

[Claims] (1) Set the upper and lower limits of the modulation frequency, and determine the polarity of the indication of the phase measurement system displayed by sequentially sweeping the modulation section, and determine the absolute phase amount by counting the number of times it exceeds 2π. A method for measuring the absolute length of a transmission line, characterized in that the absolute length is measured by (2) a first oscillator that outputs a modulated signal;
a modulating section having means for splitting the signal output from the second oscillator into two; a demodulating section having the second oscillator and for converting the split signal into an IF multiplied signal; a measuring section for measuring the phase difference of the signal, a means for controlling the frequency of the modulating section and the demodulating section, a means for determining the polarity of the instruction of the measuring section, a means for calculating the absolute phase amount, and a means for determining the absolute phase amount from the absolute phase amount. and a control section having means for increasing the length, inputting one of the two branched signals to the transmission line under test, and guiding the output of the transmission line under test to the demodulation section. A device for measuring the absolute length of a transmission line.